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Replacing the Rear Axles

on the 1985 300D (W123)

by dmorrison


My son’s 1985 300D’s rear axle was making noise. The outer boots, inner clamp, was loose and I’m sure some or all of the oil was gone. He started to get a clicking noise upon de-acceleration so I knew it was time for a new axle. The seals were fine once I disassembled the differential so I chose not to replace them. The axles are made in China so we shall see how they perform.

One word of caution. The wheel hub to axle bolt spacer that was provided was longer than the one on the car. Measure these carefully and IF the axles are original to the car or have been there a long time, reuse the spacer tube that you remove, otherwise the axle will not completely seat into the hub. I also had the bolt provided break while installing it. So I would reuse what Mercedes provided.

Place chocks under the rear of the FRONT tires since you will be jacking up the rear tires.

Jack the car up using the differential. I have a long body jack and it is easy to raise the car from the rear bumper area.

As you can see I have placed the jack stands under the sub frame bushing area. I find this to be a safe and secure place for the stands. After you have settled the car onto the stands, give the car a good shake and make sure the stands have not changed position under the car. If they have in anyway moved, reposition the jacks stands.

Since you will be opening the rear of the differential, either pressure wash it or use a degreaser and a brush as shown. I completely pressure washed the car back in October when we got it. So the car was pretty clean and only required a brushing.

Remove the fill plug in the differential (14MM Allen socket). Always a good idea to remove the fill plug first, instead of the drain plug. You would hate to find out the fill plug is stuck after draining the oil. I am going to reuse the installed synthetic oil since we installed it last November. We filtered it and reused it.

Remove the drain plug and collect the oil. ( 14MM Allen socket)

Remove the wheel hub to axle bolts as shown. ( 13MM socket ). Save the tube spacer.

Using a brass drift, pound out the axle from the hub. CAUTION, do not let the axle fall. Attach the axle to a wire hanging from the anti sway bar.

Remove the caliper from the wheel hub ( 19MM socket) and hang it with wire to the anti sway bar. Do not let it hang by the hose, you will ruin the hose.

Support the differential with a jack. An adjustable jack, not a jack stand. You will have to raise and lower the differential a few inches during this job. Make sure you do not block the rear cover of the differential, it must come off.

Remove the bolts holding the rear differential cover to the bushing as shown. (22MM socket).

To get to the upper bolt, push the sway bar up and out of the way of the socket. The sway bar is flexible and will move easily.

Using an extension remove the bushing to floor bolts and remove the bushing. (13 MM socket )

Remove the differential rear cover bolts. (15MM socket)except the one next to the breather tube it was 17MM. You may have to lower the differential to get to the top bolts.

To break the seal on the differential rear cover caused by the RTV sealant, I used a punch as shown in the hole provided near the drain hole. A few taps with a hammer will break the seal and the cover can be pealed off the differential.

To remove the C clips I used this hooked scratch all I got from Harbor Freight ( item 93958-2VGA). Pull on the clips hole in the tab and the C clip come out of the axle shaft. Watch out it will go flying if done this way. So be ready to catch it or it will be about 5 feet behind the car. I recommend doing one axle at a time so clips, washers, and spacers are not mixed up.
You may have to rotate the axles to find the C clip tab. The c clip can rotate on the axle.

Remove the axle by just pulling it towards the wheel hub, yes you will have to direct it around the wheel hub, but it will move easily.Once the axle is removed, carefully clean the axle to differential seal. Do not allow dirt and particles to enter the differential. As you can see mine are in very good shape. So even though I had a set I choose not to replace them. Replacing them is just like any seal. A seal puller is best to remove it. Apply gear oil to the seal and press it in. Refer to the manual on depth of the seals position.

Remove the spacing ring from the old axle and place it on the new one. You may have to file the inside of the spacer opening to remove any burs that interfere with its installation. Spacer rings are specific to the axle side, DO NOT SWAP THEM. You should reuse the old spacer. It was specifically installed based on the differential adjustment to place the axle in the correct position in its opening. As long as you don’t mess with the differential gear adjustment you should not have to change the spacing ring.

Lube the axle seal with gear oil and insert the axle into the differential opening. Press it in as hard as you can. Look at the axle in the differential where the C clip attaches you should see the slot for the c clip.
Concerned with losing the c clip I attached a wire to the tab hole and then installed the C clip. If it went flying I could easily retrieve it from inside the differential.

NOTE: the axle/C clip fitting should be snug, NOT LOOSE

I pressed in the C clip as far as I could with my fingers and then used a punch and hammer to drive it all the way in. I did this by tapping on either side of the tab.

Make sure the tab is completely inserted into the axle slot. You want to make sure the C clip did not spread and is on top of the axle. You want it in the slot provided. I rotated the axle to see the end of the C clip and make sure it is in the slot. Do this for both ends of the C clip.

I’m showing the installed clip compared to the uninstalled to allow you to see the tabs on the end of the C clip. Those tabs must not be visible. They should be buried in the slot.

C clip for the passengers side axle. I replaced both axles.

Clean the differential to cover mating surface. I used degreaser and a putty knife. Protect the gears by not allowing any debris to get into the differential.

Start by RTVing the cover and allowing it to skin over. Usually about 10 minutes, but follow the package instructions. Install the cover and bolts. (45 NM torque )

Attach the rear differential bushing to the cover.( 120 NM torque )

Attach the rear bushing to the trunk floor ( 25NM torque )

Install the Calipers on the wheel hubs using Loctite. ( 90NM torque)

Install the axle shaft to wheel hub bolts. (30NM torque 8mm bolt, 95 Nm 12mm bolt)

Install wheels and torque to 110NM.

After your RTV has cured (12-24 hours ) you can install your differential oil ( 1 liter of oil ) and your fill plug ( 50 NM torque). Consider using anti seize paste on the threads for future oil changes.

Tools used, part one

Complete socket set (up to 22mm)
½” drive ratchet
3/8” drive ratchet
½”Breaker bar
½” and 3/8” extensions
Torque wrench
Flash light
Hooked screwdriver
Long needle nose pliers
Putty knife

Tools used, part two

Degreaser and towels
Allen socket set
Diagonal cutters
3/8” socket set
Brass drift
Needle nose locking pliers



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